Impulse discriminating system



April 30, 1940. D. HERMANN I IMPULSE DISCRIMINATING SYSTEM- 2 Sheets-Sheet 1 Filed July 1. 1938 M mm m /M64 2 m m Y u m m a F. g MW NHM hm 1 T T 06 JHME my #06 MM 3 4-H al WE HI. w MM WWW v 5 IA 5 1-7 "A m 1 y MW. L mmm mwm NUAIII Ill-fir ELF MEL v MHM U w9 Z6 5 .56 MW 1 Z 1 I/ FWF. o lwks HI. J ww USW TIME lNVl ENTOR D. HERMAN/V ws ATTORNEYS April 4 I I D. HERMA NN I 2.199.202

' IMPULSE DISCRIMINATING SYSTEM v Filed July 1 1938 g Sheets-Sheet 2 ail INVENTOR 0. HERMAN BY ATTORNEYS I Patented'fipr. 30, 1940 IMPULSE DISORIMINATING SYSTEM Dietrich Hermann, Berlin, Germany, assignor to Telefunken Gesellschaft i'iir Drahtiose Telegraphic 111. b. 11., Berlin, Germany, a corporation of Germany Application July 1, 1938, Serial No. 216,995

\ In Germany July 1, 1937 2 Claims. (01. 178-695) In television'receiver apparatus in which the picture is re-created by a Braun cathode-ray tube, -ways and means must be provided which will distinguish between the line impulses, frame impulses and the picture (subject-matter) signals in order to insure proper coordination of transmission. These devices form the sweep or de-' flector means of the receiver. They are subject to the control action of synchronizing signals of 1 the transmitter, and they build up the line raster,

subject to the intensity distribution or modulation ofthe picture signal.

In what follows the systems considered shall only be the so-called single-channel synchroni- 15 zation, in other words, transmission systems in which the various signals controlling and causing deflection of the cathode-ray pencil in both coordinate senses are mixed. The various signals or impulses hereinafter called line and frame 20 impulses serve to control difierent deflection means (line and frame deflection or sweep, or line-sequence deflection in the interlaced-scanning method). Hence, they must be separated or sorted out from the-mixture in order that they 25 may be brought to act separately at the devices synchronizing impulses according to the method.

'shown' in Figure 2;

40 Figure 6 shows a modification of Figure 3, and

Figure '7 shows a modification of the system shown in Figure 5.

- Fundamentally, two diiferent ways are adapted.

to the said end which shall be explained by ref- 45 erence to the schematic Figures 1 and 2. In the case of Figure 1 the mixture of impulses is simultaneously fed to the two sweep arrangements.

. But the frame deflector means reacts only to picture or frame'impulses, while the line sweep 50 means respondsto both line and frame impulses.

Reaction to line impulses is desired, and the frame impulse stops line deflection control only for the time it lasts. In the case illustrated in Figure2 the line and the frame deflection are in no sequence along the line. The impulse mixture is fed to the line deflection means; the latter responds in the desired manner to line impulses, while the disturbance caused in the line deflection generator upon the arrival of a frame-- impulse serves here for initiating andcausing the 5 frame deflection, that is, to separate the impulses. Two practical embodiments of these two cases shall be explained hereinafter by reference to Figures 3 and 5.- The impulse mixture'is fed to the control grid of a Thyratron I, Figure 3. The

' plate lead of this Thyratron includes a resistance {through which a condenser 3 is charged. Upon each line impulse a flow of current in the Thyratron occurs and as a resultthe condenser 3 is discharged. The saw-tooth voltage wave set up at the same is impressed upon a pair of deflector plates of the Braun or cathode ray tube or else, where magnetic sweep means are involved, it serves for the production or control of a sawtooth shaped deflector current.- From the control grid of the Thyratron I a lead is brought by way of a resistance. 4 to the control grid-5 of a Thyratron 6. Between the control grid 5 and the ground potential 'is connected a con'- denser I. The time constant of the resistancecondenser combination 4, 1 is so proportioned that the voltage impulses arising at the control -grid 5 by incoming line impulses will not suflice to render the Thyratron 6 conducting. But if a frame impulse arrives which, so far as its length or duration is concerned, is equal to a plurality of line impulses, the control grid 5 will be caused to assume such a high potential that the Thyratron 6 is actually made conducting. This potential and its shape at the control grid 5 is shown in Figure 4 together with the impulse mixture, the dash-line indicating the grid potential at which the Thyratron is made conducting. When a current flows therethrough, then the condenser 8 which was'charged up through 40 the resistance 9 isdischarged, and the saw-tooth potential wave arising at the condenser 8 is fed to the second deflector plate pair of the Braun cathode-ray tube.

capacitively to the control grid of tube l3. The 5 latter in this scheme plays the part of a reverser tube. Its plate is in capacitive coupling relation with the control grid of the frame frequency Thyratron l4. Condenser i6 is charged through the plate resistance I of Thyratron ll. The sawtooth voltage wave at the said condenser serves for deflection. The grid of Thyratron I4 is at a potential so that with the positive impulse which is imparted to it for a brief instant upon discharge of condenser I! through tube l3 occasioned by a line impulse will not be .capable of unblocking or rendering conductive the Thyratron. But, if, then, a picture or frame impulse reaches the tube Ill, the result will be that the condenser l2 discharges much more completely or longer and thus to a lower potential level. Incidentally, the current through the tube l3 becomes much smaller than before. The voltage at the plate rises to a far higher value. The grid of the Thyratron M consequently 'becomes more markedly positive. The Thyratron then becomes conducting and this causes discharge of the condenser I6.

The sweepor deflection process consists of two phases being essentially different from each other. During the charging of the condenser (for instance, 3, Figure 3) the cathode-ray pencil is slowly swept over the screen of the Braun tube in proportion to the growth of its potential. During this interval or period of time the deflector tube (I, Figure 3) is blocked. But the synchronizing impulse renders the deflector tube conducting for current. Discharge of the condenser is caused, and thereby rapid fiyback or return of the cathode-ray pencil to its origin (say, the left-hand edge of the frame) results. In

other words, it is only during the rapid return sweep that the deflector tube is operative, and it is always this phase or stage of the process which is here meant in discussing the eiIect or the activity of the deflector or- 'sweep generator or broadly the deflection.

However, the sweep schemes discussed by reference to Figures 3 and 5 basically inhere a drawback which tends to affect somewhat and impair the operation thereof. During the duration of the frame'impulses, as will be noted, the

line deflection tube, by virtue of its grid potential, is at each impulse placed in an operating or conducting state which differs from the normal state (synchronized line deflection) and which is liable to lead to serious disturbances; In the case of Figure 3 the line Thyratron I is able to experience free oscillations; and as the number of free oscillations occurring in the course of the frame impulse is neither known nor influenceable or controllable, it may happen that at the time when the compulsory or looking condition (synchronization with line impulses) is resumed, there is no way of telling what the phase situation at the line Thyratron may be.

As a result'the synchronized line "sweep under certain unfavorable circumstances may occur under unsatisfactory conditions.

the cathode of the Thyratron i.

' tivibrator, (self) amazes vention whereby the line sweep generator, during the duration of the frame impulse or the line-sequence impulse, is rendered inoperative once the frame deflection has been initiated. This is insured by producing an impulse from the frame deflection tube which conducts current during the frame deflection which persists still about the end of'the frame impulse which happens to be active and which serves for producing the blocking effect in the line deflection arrangement.

Hence, the circuits illustrated in Figures 3 and 5 may be improved upon in a simple way as shown in Figures 6 and 7. In series with the cathode of the Thyratron 6 is connected a resistance IT. The cathode itself is connected with When current flows through the Thyratron 6, a positive potential is set up across the resistance l'l; this positive potential will so influence the potential situation between the control grid and the cathode of Thyratron i that the latter stays blocked.

Similarly, in the second circuit scheme (see Figure 7) a resistor I8 is connected in series with the cathode of Thyratron i4, and the cathode of the latter tube is united again with the cathode of tube I 6. Also in this instance, while the frame impulse lasts, a positive potential is built up across resistor l8 whereby the Thyratron is .biased and blocked.

It will be evident that the step here suggested (introduction of a cathode resistor) is not the I only feasible and conceivable solution adapted to or scan generator is influenced by the frame or picture deflection generator during the frame impulse period, is not restricted to the circuit organizations illlustrated in Figures 3 and 5.

In all deflection generators whether of the mulblocking oscillator or other types, fundamentally three groups may be distinguished:

I. Deflector or sweep voltage generating means subject to outside excitation or control action.

Each individual phase of a cycle or action is occasioned by the control; inoperative in the absence of such control. "II. Excited deflector means. These are impacted ,or impulsed once by a signal, say, a synchronizing signal for initiation of the cycle or action. Thus, the signal merely starts theaction or cycle, and it has no further influence on the cycle; and once the latter 'is terminated, the deflector means is again rendered inoperative.

' III. Self-oscillating deflector generators. These produce the desired periodic motions in a perfectly spontaneous way; the synchronizing signals serve solely to keep them in step with a prescribed frequency. The synchronization, however, exercises no influence upon the nature and the conditions of the action.

It will be noted that the present invention is concerned with sweep generators belonging to groups II and III. It will be evident in this connection that a deflector arrangement pertaining to group III byv slight modifications can be converted'into one that will fall in group II, since all of the sweep circuitarrangements here concerned and discussed comprise controlled discharge vessels (Thyratrons). The control action is insured by the agency of a control grid, and the potential of the latter may be so set that the generator just falls short of the point where it is able to oscillate freely, though being adapted to be changed into the oscillatory state by the action of synchronizing signals or pulses. on the other hand, a line sweep generator which belongs in group II and which, therefore, is incapable of free oscillation in the intervals between line impulses is changed into a generator of group 111 during the period that the frame impulse lasts. For it will be seen that the control grid then has permanently a potential such that the generator is able to experience free oscillatlons. In other words, the steps and means here disclosed are necessary also for generators group m.

At all events it will be possible to derive from the frame or picture impulse which is acting a given instant (for instance, at the frame sweep generator) a voltage capable of blocking the line deflection generator for the length of time the frame impulse lasts. If in the deflector arrangements are comprised the so-called blocking os cillatorafthen, in addition, there is a chance for wherein line and frame synchronizing impulses of dlil'erent time duration and frequency are transmitted includinga system for diiferentiating between the impulses comprising a pair of discharge tubes each having an anode, a control 5 electrode and a cathode, means for applying both line and frame impulses to the control electrode of one of the tubes, means including a time constant circuit for applying frame impulses to the control electrode of the other tube, and means controlled by the conductivity of said other tube for controlling the relative grid-cathode potential of said one tube -to render said one tube blocked during periods of conductivity of said other tube. V

2. In a synchronizing system for television wherein line .and frame synchronizing impulses of different time duration and frequency are transmitted including a system for differentiating between the impulses comprising a pair of dis- 20 charge tubes each having an anode, a control electrode and a cathode, means for applying both line and frame impulses to the control electrode of one of the tubes, means including a series connected resistance and condenser for applying :5 frame impulses to the control electrode of'the 1 other tube, means including a cathode resistance associated with said other tube effective to maintain' said one tube non-conductive regardless of the impulses applied to the control electrode & of said one tube during periods when said other tube is conductive, and means for developing separate voltages of saw-tooth wave form fromeach of said tubes.

DIE-TRICK W. Q 

